I am re-doing my kitchen and am going to replace a stainless steel 7" deep double sink with an under counter mount sink 9" deep double sink. I anticipate a problem with it being too low to properly drain. 9" below the discharge pipe there is a plug (I assume that it's a clean out). Can I use this for the discharge pipe and just cap the existing one up above? I'm not certain of how I would configure this to accommodate the p-trap etc. Would it have to go below the now lowered discharge pipe? I would only have about 5" between the new lower discharge pipe and the floor of the existing cabinet. I am having new cabinets built and could ask for a cut-out if the p-trap had to go lower. I'm having a problem figuring out how to plumb this project. Thanks for any and all advice. Incidentally that rusted up plug has never been removed in my 30 years of living here. That might be a project in itself... and then if the threads are still good..? I could send photos if someone would be needing to see exactly what I'm up against.

I am re-doing my kitchen and am going to replace a stainless steel 7" deep double sink with an under counter mount sink 9" deep double sink. I anticipate a problem with it being too low to properly drain. 9" below the discharge pipe there is a plug (I assume that it's a clean out). Can I use this for the discharge pipe and just cap the existing one up above? I'm not certain of how I would configure this to accommodate the p-trap etc. Would it have to go below the now lowered discharge pipe? I would only have about 5" between the new lower discharge pipe and the floor of the existing cabinet. I am having new cabinets built and could ask for a cut-out if the p-trap had to go lower. I'm having a problem figuring out how to plumb this project. Thanks for any and all advice. Incidentally that rusted up plug has never been removed in my 30 years of living here. That might be a project in itself.... and then if the threads are still good.....????? I could send photos if someone would be needing to see exactly what I'm up against.
You can not use the OTHER clean out... To solve your problem go to any hardware store and ask them for two flanged tailpiece and cut them down to the size that you need you shouldn't have to adjust any of the other pipes on the length any way. The problem are the ones that you need to look at.